View file Universal billing/plugins/payment/tpl/payeer.tpl.php

<?
$data = array(
	$M_SHOP_ID,
	$pay_id,
	$pay_cost,
	'RUB',
	base64_encode($pay_desc),
	$SECRET_KEY
);

$hash = strtoupper(hash('sha256', implode(':', $data)));
?>
<form id="payment" name="payment" action="//payeer.com/merchant/" method="GET">
	<input type="hidden" name="m_shop" value="<?= $M_SHOP_ID?>" />
	<input type="hidden" name="m_orderid" value="<?= $pay_id?>" />
	<input type="hidden" name="m_amount" value="<?= $pay_cost?>" />
	<input type="hidden" name="m_curr" value="RUB" /> 
	<input type="hidden" name="m_desc" value="<?= base64_encode($pay_desc)?>" />
	<input type="hidden" name="m_sign" value="<?= $hash?>" />
  <button type="submit" name="m_process" class="btn btn-success"><?= __('Оплатить')?> <?= $pay_cost?> руб.</button>
</form>